Abstract
We examined the relationship between continental-level genetic ancestry and racial and ethnic identity in an admixed population in New Mexico with the goal of increasing our understanding of how racial and ethnic identity influence genetic substructure in admixed populations. Our sample consists of 98 New Mexicans who self-identified as Hispanic or Latino (NM-HL) and who further categorized themselves by race and ethnic subgroup membership. The genetic data consist of 270 newly-published autosomal microsatellites from the NM-HL sample and previously published data from 57 globally distributed populations, including 13 admixed samples from Central and South America. For these data, we 1) summarized the major axes of genetic variation using principal component analyses, 2) performed tests of Hardy Weinberg equilibrium, 3) compared empirical genetic ancestry distributions to those predicted under a model of admixture that lacked substructure, 4) tested the hypotheses that individuals in each sample had 100%, 0%, and the sample-mean percentage of African, European, and Native American ancestry. We found that most NM-HL identify themselves and their parents as belonging to one of two groups, conforming to a region-specific narrative that distinguishes recent immigrants from Mexico from individuals whose families have resided in New Mexico for generations and who emphasize their Spanish heritage. The “Spanish” group had significantly lower Native American ancestry and higher European ancestry than the “Mexican” group. Positive FIS values, PCA plots, and heterogeneous ancestry distributions suggest that most Central and South America admixed samples also contain substructure, and that this substructure may be related to variation in social identity. Genetic substructure appears to be common in admixed populations in the Americas and may confound attempts to identify disease-causing genes and to understand the social causes of variation in health outcomes and social inequality.
Highlights
Admixed populations form when individuals from previously separated populations mate with one another
Social-group identity and population substructure in New Mexico and Latin America underlying susceptibility to common diseases [1,2,3], and it can provide important insights into the causes of social inequality and health disparities in societies that are stratified by race or ethnicity [4,5]
The rate of migration from Mexico increased in 20th century, and today more than half of New Mexicans who identify themselves as HL on the US census identify as Mexican or Mexican American [17]
Summary
Admixed populations form when individuals from previously separated populations mate with one another. The earliest Spanish census and church records enumerated individuals of mixed ancestry as well as exclusive Spanish or Native American ancestry [12,13], indicating that mating between Spaniards and Native Americans occurred from earliest contact [12,13,14,15]. These records show that, during the colonial period (1598–1821), Spaniards used a hierarchical caste system to describe and socially rank admixed individuals according to the fraction of Spanish and Native American heritage. As a result of this region-specific history, the notion of comparatively recent Mexican vs. deep Spanish heritage is a salient feature of social identity in New Mexico today [8]
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